Syntheses, Structures, and Antimicrobial Activities of Remarkably Light-Stable and Water-Soluble Silver Complexes with Amino Acid Derivatives, Silver(I) <i>N</i>-Acetylmethioninates

Reaction of l- and dl-<i>N</i>-acetylmethionine (Hacmet) and Ag₂O in water at ambient temperature afforded the remarkably light-stable silver complexes {[Ag­(l-acmet)]}_<i>n</i> (<b>1</b>) and {[Ag₂(d-acmet)­(l-acmet)]}_<i>n</i> (<b>2</b>), respectively. The color of the solids and aqueous solutions of <b>1</b> and <b>2</b> did not change for more than 1 month under air without any shields. The light stability of these two silver­(I) complexes is much higher than that of silver­(I) methioninate {[Ag₂(d-met)­(l-met)]}_<i>n</i> (<b>3</b>) (Hmet = methionine), silver­(I) <i>S</i>-methyl-l-cysteinate {[Ag­(l-mecys)]}_<i>n</i> (<b>4</b>), and silver­(I) l-cysteinate {[Ag­(l-Hcys)]}_<i>n</i> (<b>5</b>). X-ray crystallography of <b>1</b> obtained by vapor diffusion revealed that ladder-like coordination polymers with two O- and two S-donor atoms were formed. The acetyl group of acmet^– prevents chelate formation of the ligand to the metal center, which is frequently observed in amino acid metal complexes, but allows for formation of hydrogen bonds between the ligands in the crystals of <b>1</b>. These two silver­(I) <i>N</i>-acetylmethioninates showed a wide spectrum of effective antimicrobial activities against Gram-negative bacteria (<i>Escherichia coli</i> and <i>Pseudomonas aeruginosa</i>) and yeasts (<i>Candida albicans</i> and <i>Saccharomyces cerevisiae</i>), the effectiveness of which was comparable to that of water-soluble Ag–O bonding complexes

Synthesis and Molecular Structure of a Water-Soluble, Dimeric Tri-Titanium(IV)-Substituted Wells–Dawson Polyoxometalate Containing Two Bridging (C₅Me₅)Rh²⁺ Groups

A novel trititanium­(IV)-substituted Wells–Dawson polyoxometalate (POM)-based organometallic complex, i.e., a dimeric POM containing two bridging Cp*Rh²⁺ groups (Cp* = C₅Me₅) or [{α-P₂W₁₅Ti₃O₆₀(OH)₂}₂(Cp*Rh)₂]^16– (<b>D-1</b>) with <i>C</i>_i symmetry, was synthesized in an analytically pure form by a 1:2 -molar ratio reaction of the organometallic precursor [Cp*RhCl₂]₂ with the separately prepared, monomeric trititanium­(IV)-substituted Wells–Dawson POM, “[P₂W₁₅Ti₃O₅₉(OH)₃]^9–” (<b>M-1</b>). The crystalline sample (<b>NaK-D-1</b>) of the water-soluble, mixed sodium/potassium salt of <b>D-1</b> was obtained in the 14.7% yield, which has been characterized by complete elemental analysis, TG/DTA, FTIR, single-crystal X-ray structure analysis, and solution (¹⁸³W, ³¹P, ¹H and ¹³C­{¹H}) NMR spectroscopy. Single-crystal X-ray structure analysis revealed that the two species of the protonated Wells–Dawson subunits, “[P₂W₁₅Ti₃O₆₀(OH)₂]^10‑” were bridged by the two Cp*Rh²⁺ groups, resulting in the an overall <i>C</i>_i symmetry. The Cp*Rh²⁺ groups were linked to the two terminal oxygen atoms of the titanium­(IV) sites and one edge-sharing oxygen atom of the surface Ti–O–Ti bond. The ¹⁸³W NMR of <b>D-1</b> dissolved in D₂O showed that its solution structure was represented as a dimeric POM with a formula of [{α-P₂W₁₅Ti₃O₆₀(OH)₃}₂{Cp*Rh­(OH)}₂]^16– (<b>D-2</b>) with Ci (or <i>S</i>₂) symmetry. A trititanium­(IV)-substituted Wells–Dawson POM-supported organometallic complex has never been reported so far, and thus <b>D-1</b> in the solid state and <b>D-2</b> in solution are the first example of this type of complex

Synthesis and Molecular Structure of a Novel Compound Containing a Carbonate-Bridged Hexacalcium Cluster Cation Assembled on a Trimeric Trititanium(IV)-Substituted Wells–Dawson Polyoxometalate

A novel compound containing a hexacalcium cluster cation, one carbonate anion, and one calcium cation assembled on a trimeric trititanium­(IV)-substituted Wells–Dawson polyoxometalate (POM), [{Ca₆(CO₃)­(μ₃-OH)­(OH₂)₁₈}­(P₂W₁₅Ti₃O₆₁)₃Ca­(OH₂)₃]^19‑ (<b>Ca</b>_<b>7</b><b>Ti</b>_<b>9</b><b>Trimer</b>), was obtained as the Na₇Ca₆ salt (<b>NaCa-Ca</b>_<b>7</b><b>Ti</b>_<b>9</b><b>Trimer</b>) by the reaction of calcium chloride with the monomeric trititanium­(IV)-substituted Wells–Dawson POM species “[P₂W₁₅Ti₃O₅₉(OH)₃]^9–” (<b>Ti</b>_<b>3</b><b>Monomer</b>). <b>Ti</b>_<b>3</b><b>Monomer</b> was generated in situ under basic conditions from the separately prepared tetrameric species with bridging Ti­(OH₂)₃ groups and an encapsulated Cl^– ion, [{P₂W₁₅Ti₃O₅₉(OH)₃}₄{μ₃-Ti­(H₂O)₃}₄Cl]^21– (<b>Ti</b>_<b>16</b><b>Tetramer</b>). The Na₇Ca₆ salt of <b>Ca</b>_<b>7</b><b>Ti</b>_<b>9</b><b>Trimer</b> was characterized by complete elemental analysis, thermogravimetric (TG) and differential thermal analyses (DTA), FTIR, single-crystal X-ray structure analysis, and solution ¹⁸³W and ³¹P NMR spectroscopy. X-ray crystallography revealed that the [Ca₆(CO₃)­(μ₃-OH)­(OH₂)₁₈]⁹⁺ cluster cation was composed of six calcium cations linked by one μ₆-carbonato anion and one μ₃-OH^– anion. The cluster cation was assembled, together with one calcium ion, on a trimeric species composed of three tri-Ti­(IV)-substituted Wells–Dawson subunits linked by Ti–O–Ti bonds. <b>Ca</b>_<b>7</b><b>Ti</b>_<b>9</b><b>Trimer</b> is an unprecedented POM species containing an alkaline-earth-metal cluster cation and is the first example of alkaline-earth-metal ions clustered around a titanium­(IV)-substituted POM

Silver- and Acid-Free Catalysis by Polyoxometalate-Assisted Phosphanegold(I) Species for Hydration of Diphenylacetylene

A DMSO-soluble intercluster compound consisting of a tetra­{phosphanegold­(I)}­oxonium cation and an α-Keggin polyoxometalate (POM) anion, [{Au­(PPh₃)}₄(μ₄-O)]₃­[α-PW₁₂O₄₀]₂ (<b>1</b>), was found to be an effective precatalyst for the silver- and acid-free catalysis of diphenylacetylene hydration (0.67 mol % catalyst; conversions 36.1%, 55.2%, and 93.7% after 4, 6, and 24 h reactions, respectively). The reaction proceeded in the suspended system in 6 mL of 1,4-dioxane/water (4:1) at 80 °C because of the low solubility of <b>1</b>. Similar POM-based phosphanegold­(I) compounds [{{Au­(PPh₃)}₄(μ₄-O)}­{{Au­(PPh₃)}₃(μ₃-O)}]­[α-PW₁₂O₄₀]·EtOH (<b>5</b>), which is composed of a heptakis­{triphenylphosphanegold­(I)}­dioxonium cation and an α-Keggin POM anion, and [Au­(CH₃CN)­(PPh₃)]₃­[α-PMo₁₂O₄₀] (<b>6</b>), which consists of an acid-free monomeric phosphanegold­(I) acetonitrile cation and an α-Keggin molybdo-POM anion, also exhibited acid-free catalysis for the hydration of diphenylacetylene. An induction period was observed in the catalysis by <b>5</b>. On the other hand, their component species, or phosphanegold­(I) species without the POM anion, such as [{Au­(PPh₃)}₄(μ₄-O)]­(BF₄)₂ (<b>2</b>) and [{Au­(PPh₃)}₃(μ₃-O)]­BF₄ (<b>3</b>), and the monomeric phosphanegold­(I) complex [Au­(<i>RS</i>-pyrrld)­(PPh₃)] (<b>4</b>) (<i>RS</i>-Hpyrrld = <i>RS</i>-2-pyrrolidone-5-carboxylic acid), the last of which has been used as a precursor for the preparation of <b>1</b>, <b>5</b>, and <b>6</b>, showed poor activities in this reaction (0.67 mol % catalysts; conversions 1.8%, 1.7%, and 0.5% after 24 h reactions, respectively). However, upon adding the free-acid form of Keggin POM, i.e., H₃[α-PW₁₂O₄₀]·7H₂O (H-POM: 0.67 mol %), <b>2</b>–<b>4</b> exhibited remarkably enhanced activities (conversion 97.6% each after 24 h reactions). In contrast, the activities were not enhanced after adding either the sodium salt of the Keggin POM, Na₃[α-PW₁₂O₄₀]·8H₂O (Na-POM; 0.67 mol %), or a Brønsted acid 10% HBF₄ aqueous solution (0.67 mol %). Both H-POM and Na-POM themselves exhibited no activity. Catalysis by the phosphanegold­(I) species for diphenylacetylene hydration was influenced significantly under the free-acid form or sodium salt of the Keggin POM. Acid-free catalytic hydration by <b>1</b> of other alkynes, such as phenylacetylene and 1-phenyl-1-butyne, was also examined

Polyoxometalate-Assisted, One-Pot Synthesis of a Pentakis[(triphenylphosphane)gold]ammonium(2+) Cation Containing Regular Trigonal-Bipyramidal Geometries of Five Bonds to Nitrogen

Novel intercluster compounds consisting of pentakis­[(triphenylphosphane)­gold]­ammonium­(2+) cation (<b>1</b>) and Keggin polyoxometalate (POM) anions, i.e., {[Au­(PPh₃)]₅(μ₅-N)}₃[α-PM₁₂O₄₀]₂ (<b>1-PW</b> for M = W; <b>1-PMo</b> for M = Mo), were synthesized in 30–36% yield by one-pot reaction of the protonic acid form of the Keggin POMs, H₃[α-PM₁₂O₄₀]·<i>n</i>H₂O (<i>n</i> = 13 for M = W; <i>n</i> = 15 for M = Mo) with monomeric (triphenylphosphane)­gold­(I) carboxylate [Au­(<i>RS</i>-pyrrld)­(PPh₃)] [<i>RS</i>-Hpyrrld = (<i>R</i><i>S</i>)-2-pyrrolidone-5-carboxylic acid] in the presence of aqueous NH₃ at a molar ratio of 2:15:<i>x</i> (<i>x</i> = 3 for <b>1-PW</b>; <i>x</i> = 7.5 for <b>1-PMo</b>). These compounds resulted from the nitrogen-centered phosphanegold­(I) clusterization of in situ generated monomeric phosphanegold­(I) units, [Au­(PPh₃)]⁺ or [Au­(L)­(PPh₃)]⁺ (L = NH₃ or solvent), during the carboxylate elimination of [Au­(<i>RS</i>-pyrrld)­(PPh₃)] in the presence of the Keggin POMs and aqueous NH₃. The products <b>1-PW</b> and <b>1-PMo</b> were characterized by elemental analysis, Fourier transform infrared, thermogravimetric and differential thermal analyses (TGA/DTA), X-ray crystallography, and solid-state cross-polarization magic-angle-spinning (CPMAS) (³¹P and ¹⁵N) and solution (³¹P­{¹H} and ¹H) NMR spectroscopy. The lattice contained three independent {[Au­(PPh₃)]₅(μ₅-N)}²⁺ cations, of which two took regular trigonal-bipyramidal (TBP) geometries and the third took a distorted, square-pyramidal (SP) geometry. These geometries are in contrast to those reported by Schmidbaur’s group for {[Au­(PPh₃)]₅(μ₅-N)}²⁺ cations as BF₄ salts. Density functional theory and ONIOM calculations for {[(L₃P)­Au]_<i>n</i>N}^{(<i>n</i>−3)+} (L = H or Ph; <i>n</i> = 4–6) showed that the pentacoordinate cluster is energetically most stable and its TBP structure is only 1.6 kcal mol^–1 more stable than its SP structure, in accordance with the experimental facts